From ab9d306d9c3bf64b1dbad127aa13252cc550f839 Mon Sep 17 00:00:00 2001 From: Sergey Senozhatsky Date: Tue, 8 Sep 2015 15:04:41 -0700 Subject: [PATCH] zsmalloc: use shrinker to trigger auto-compaction Perform automatic pool compaction by a shrinker when system is getting tight on memory. User-space has a very little knowledge regarding zsmalloc fragmentation and basically has no mechanism to tell whether compaction will result in any memory gain. Another issue is that user space is not always aware of the fact that system is getting tight on memory. Which leads to very uncomfortable scenarios when user space may start issuing compaction 'randomly' or from crontab (for example). Fragmentation is not always necessarily bad, allocated and unused objects, after all, may be filled with the data later, w/o the need of allocating a new zspage. On the other hand, we obviously don't want to waste memory when the system needs it. Compaction now has a relatively quick pool scan so we are able to estimate the number of pages that will be freed easily, which makes it possible to call this function from a shrinker->count_objects() callback. We also abort compaction as soon as we detect that we can't free any pages any more, preventing wasteful objects migrations. Signed-off-by: Sergey Senozhatsky Suggested-by: Minchan Kim Acked-by: Minchan Kim Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/zsmalloc.c | 78 +++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 78 insertions(+) diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c index b7b4a5612ec7..27b9661c8fa6 100644 --- a/mm/zsmalloc.c +++ b/mm/zsmalloc.c @@ -246,6 +246,14 @@ struct zs_pool { atomic_long_t pages_allocated; struct zs_pool_stats stats; + + /* Compact classes */ + struct shrinker shrinker; + /* + * To signify that register_shrinker() was successful + * and unregister_shrinker() will not Oops. + */ + bool shrinker_enabled; #ifdef CONFIG_ZSMALLOC_STAT struct dentry *stat_dentry; #endif @@ -1778,6 +1786,69 @@ void zs_pool_stats(struct zs_pool *pool, struct zs_pool_stats *stats) } EXPORT_SYMBOL_GPL(zs_pool_stats); +static unsigned long zs_shrinker_scan(struct shrinker *shrinker, + struct shrink_control *sc) +{ + unsigned long pages_freed; + struct zs_pool *pool = container_of(shrinker, struct zs_pool, + shrinker); + + pages_freed = pool->stats.pages_compacted; + /* + * Compact classes and calculate compaction delta. + * Can run concurrently with a manually triggered + * (by user) compaction. + */ + pages_freed = zs_compact(pool) - pages_freed; + + return pages_freed ? pages_freed : SHRINK_STOP; +} + +static unsigned long zs_shrinker_count(struct shrinker *shrinker, + struct shrink_control *sc) +{ + int i; + struct size_class *class; + unsigned long pages_to_free = 0; + struct zs_pool *pool = container_of(shrinker, struct zs_pool, + shrinker); + + if (!pool->shrinker_enabled) + return 0; + + for (i = zs_size_classes - 1; i >= 0; i--) { + class = pool->size_class[i]; + if (!class) + continue; + if (class->index != i) + continue; + + spin_lock(&class->lock); + pages_to_free += zs_can_compact(class); + spin_unlock(&class->lock); + } + + return pages_to_free; +} + +static void zs_unregister_shrinker(struct zs_pool *pool) +{ + if (pool->shrinker_enabled) { + unregister_shrinker(&pool->shrinker); + pool->shrinker_enabled = false; + } +} + +static int zs_register_shrinker(struct zs_pool *pool) +{ + pool->shrinker.scan_objects = zs_shrinker_scan; + pool->shrinker.count_objects = zs_shrinker_count; + pool->shrinker.batch = 0; + pool->shrinker.seeks = DEFAULT_SEEKS; + + return register_shrinker(&pool->shrinker); +} + /** * zs_create_pool - Creates an allocation pool to work from. * @flags: allocation flags used to allocate pool metadata @@ -1863,6 +1934,12 @@ struct zs_pool *zs_create_pool(char *name, gfp_t flags) if (zs_pool_stat_create(name, pool)) goto err; + /* + * Not critical, we still can use the pool + * and user can trigger compaction manually. + */ + if (zs_register_shrinker(pool) == 0) + pool->shrinker_enabled = true; return pool; err: @@ -1875,6 +1952,7 @@ void zs_destroy_pool(struct zs_pool *pool) { int i; + zs_unregister_shrinker(pool); zs_pool_stat_destroy(pool); for (i = 0; i < zs_size_classes; i++) { -- 2.20.1